Linyi Bian

Core–sheath structured bacterial cellulose/polypyrrole nanocomposites with excellent conductivity as supercapacitors

Core–sheath structured conductive nanocomposites were prepared by wrapping a homogenous layer of polypyrrole (PPy) around bacterial cellulose (BC) nanofibers via in situ polymerization of self-assembled pyrrole. By manipulating the ordered core–sheath nanostructure, BC/PPy nanocomposites were achieved and outstanding electrical conductivity as high as 77 S cm−1 was obtained with the optimized reaction protocols, i.e., feeding mass ratio of BC/Py 1 : 10, molar ratio of FeCl3/Py 0.5 : 1, molar ratio of HCl/Py 1.2 : 1, volume ratio of DMF–H2O 1 : 2, reaction temperature 0 °C, and reaction time 6 h. The BC/PPy nanocomposites demonstrated promising potential for supercapacitors, with a highest mass specific capacitance hitting 316 F g−1 at 0.2 A g−1 current density. The whole-optimized protocol in preparing highly conductive PPy/BC composites may be readily extended to the preparation of new conductive materials based on core–sheath structured BC nanocomposites for various technological applications.

Naphthodifuran alternating quinoxaline copolymers with a bandgap of ∼1.2 eV and their photovoltaic characterization

Four new alternating copolymers of naphthodifuran and quinoxaline have been developed. With the bandgap as low as 1.2 eV, polymers exhibited extended absorption to 1200 nm. Their potential in bulk heterojunction solar cells was evaluated. With device optimization, triazoloquinoxaline based polymers contributed the highest power conversion efficiency of 0.84%.

Design and synthesis of triazoloquinoxaline polymers with positioning alkyl or alkoxyl chains for organic photovoltaics cells

Four benzodithiophene-triazoloquinoxaline alternating polymers, PBDTT-BTzQx-EH-C1, PBDT-BTzQx-EH-C1, PBDT-BTzQx-EH-C12 and PBDT-BTzQx-C12, have been designed and synthesized to investigate the correlation of alkyl side chains with the opto-electronic properties of the resulting polymers. The introduction of side chains onto the thiophene spacer or quinoxaline unit lowers the highest occupied molecular orbital energy level of the polymers, while excessive chains prevent the polymer backbone from π–π stacking and result in a decreased short circuit current and fill factor in a photovoltaic application. The bulk heterojunction cells fabricated by blending PBDTT-BTzQx-EH-C1 with [6,6]-phenyl-C61-butyric acid methyl ester exhibit a best power conversion efficiency (PCE) of 1.40%, with a short-circuit current density of 4.12 mA cm−2, an open-circuit voltage of 0.62 V and a fill factor of 55%. The device was further optimized to 2.24% PCE by using PFN (5 nm)/Ca (5 nm) as a co-interfacial layer.

Direct access to 4,8-functionalized benzo[1,2-b:4,5-b′]dithiophenes with deep low-lying HOMO levels and high mobilities

A general methodology has been proposed for the straightforward access to 4,8-functionalized benzo[1,2-b:4,5-b′]dithiophenes (BDTs) via Pd mediated coupling reactions including Suzuki–Sonogashira coupling and carbon–sulfur bond formation reactions. This versatile platform can be used to construct a library of BDT core centred conjugated systems, featuring large fused-ring structure and good charge mobility, where a hole mobility of 0.061 cm2 V−1 s−1 is demonstrated. With the energy level fine-tuned with functionalization, the charge transporting BDTs show great potential for donor–acceptor polymers.

Side-chain Engineering of Benzo[1,2-b:4,5-b']dithiophene Core-structured Small Molecules for High-Performance Organic Solar Cells.

Three novel small molecules have been developed by side-chain engineering on benzo[1,2-b:4,5-b’]dithiophene (BDT) core. The typical acceptor-donor-acceptor (A-D-A) structure is adopted with 4,8-functionalized BDT moieties as core, dioctylterthiophene as π bridge and 3-ethylrhodanine as electron-withdrawing end group. Side-chain engineering on BDT core exhibits small but measurable effect on the optoelectronic properties of small molecules. Theoretical simulation and X-ray diffraction study reveal the subtle tuning of interchain distance between conjugated backbones has large effect on the charge transport and thus the photovoltaic performance of these molecules. Bulk-heterojunction solar cells fabricated with a configuration of ITO/PEDOT:PSS/SM:PC71BM/PFN/Al exhibit a highest power conversion efficiency (PCE) of 6.99% after solvent vapor annealing.

Correlation of structure and photovoltaic performance of benzo[1,2-b:4,5-b′]dithiophene copolymers alternating with different acceptors

Four π-conjugated benzo[1,2-b:4,5-b′]dithiophene (BDT) based polymers were synthesized for application in polymer solar cells. These polymers possessed desirable HOMO/LUMO levels for polymer photovoltaic applications. PBDTT–TTz and PBDTT–DTBT displayed strong absorption in the range of 300–650 nm, while PBDTT–DPP and PBDTT–TTDPP showed a further 100 nm extended absorption band. The lowest unoccupied molecular orbital energy levels of polymers were tuned effectively from −3.34 eV to −3.81 eV by fusing with different accepting units. A maximum power conversion efficiency of 2.60% was obtained from photovoltaic cells with a PBDTT–TTz : PC61BM (1 : 2, w/w) blend film as the active layer, with a short circuit current density of 8.37 mA cm−2, an open circuit voltage of 0.70 V, and a fill factor of 44.3%.

A versatile strategy to directly synthesize 4,8-functionalized benzo[1,2-b:4,5-b′]difurans for organic electronics

A direct synthesis of 4,8-functionalized benzo[1,2-b:4,5-b′]difurans (BDFs) is developed. By fine-tuning the energy levels with different 4,8-functionalities or incorporating with electron-accepting units, BDFs show great potential as organic electronic materials, as demonstrated by 4.61% power conversion efficiency for polymer solar cells.

Two-dimensional narrow bandgap conjugated polymers for high-efficiency solar cells

In this paper, the design principle for two-dimensional conjugated polymers in which high hole-transporting polymer backbone grafted with accepting side chains is illustrated. Some successful fluorene and carbazole based polymers are summarized and compared to give an insight on the structure design and bandgap engineering for high-efficiency solar cells.

Towards High-Efficiency Organic Solar Cells: Polymers and Devices Development

The effective conversion of solar energy into electricity has attracted intense scientific interest in solving the rising energy crisis. Organic solar cells (OSCs), a kind of green energy source, show great potential application due to low production costs, mechanical flexibility devices by using simple techniques with low environmental impact and the versatility in organic materials design (Beal, 2010). In the past years, the key parameter, power conversion efficiencies (PCE), is up to 7% under the standard solar spectrum, AM1.5G (Liang et al., 2010). The PCE of solar cells are co-determined by the open circuit voltage (Voc), the fill factor (FF) and the short circuit density (Jsc). Researchers have made great efforts in both developing new organic materials with narrow band gap and designing different structural cells for harvesting exciton in the visible light range. Solution processing of π-conjugated materials (including polymers and oligomers) based OSCs onto flexible plastic substrates represents a potential platform for continuous, largescale printing of thin-film photovoltaics (Krebs, 2009; Peet, 2009). Rapid development of this technology has led to growing interest in OSCs in academic and industrial laboratories and has been the subject of multiple recent reviews (Cheng, 2009; Dennler, 2009; Krebs, 2009; Tang, 2010). These devices are promising in terms of low-cost power generation, simplicity of fabrication and versatility in structure modification. The structure modification of πconjugated materials has offered wide possibilities to tune their structural properties (such as rigidity, conjugation length, and molecule-to-molecule interactions) and physical properties (including solubility, molecular weight, band gap and molecular orbital energy levels). This ability to design and synthesize molecules and then integrate them into organic–organic and inorganic–organic composites provides a unique pathway in the design of materials for novel devices. The most common OSCs are fabricated as the bulkheterojunction (BHJ) devices, where a photoactive layer is casted from a mixture solution of polymeric donors and soluble fullerene-based electron acceptor and sandwiched between two electrodes with different work functions (Yu et al., 1995). When the polymeric donor is excited, the electron promoted to the lowest unoccupied molecular orbital (LUMO) will lower its energy by moving to the LUMO of the acceptor. Under the built-in electric field caused by the contacts, opposite charges in the photoactive layer are separated, with the holes being transported in the donor phase and the electrons in the acceptor. In this way, the blend can be considered as a network of donor–acceptor heterojunctions that allows efficient